A hacker with a Guy Fawkes mask, a symbol linked to the Anonymous hacking movement. Photo: Bloomberg

"The Federal Reserve System is aware that information was obtained by exploiting a temporary vulnerability in a website vendor product," a Federal Reserve spokesman said.

"The vulnerability was fixed shortly after discovery and is no longer an issue. This incident did not affect critical operations of the Federal Reserve System." On Monday, an Anonymous-linked Twitter account called Operation Last Resort, claimed in a tweet to have obtained and posted "4k banker d0x via the FED." The group argues it is taking actions responding to the suicide last month of Aaron Swartz, an internet freedom advocate who was being prosecuted for illegally downloading millions of academic journal articles he had allegedly planned to distribute for free.